1. Field of the Invention
This invention relates to a process for producing petroleum crude from a permeable earth formation and more particularly to a material and a method for treating a subsurface permeable formation containing petroleum crude to increase petroleum crude production while preventing abrasive damage to well equipment caused by movement of materials previously used in treating subsurface permeable formations.
2. Prior Art
It has been known to inject water, gas and steam into an earth formation containing petroleum crude to increase the mobility of the crude and cause it to move to a producing location. In some field procedures the same well alternately is used for both injection and for crude production (known as huff-and-puff in a steaming operation) and in other field procedures separate injection and production walls spaced from each other through the petroleum containing formation are used. A variety of injection procedures using a variety of injection materials have been proposed most of which have the objective of increasing the volume of production of the petroleum crude at the producing well.
In the particular case of steam injection into an injection well with the objective of moving crude to a producing well, it has been observed that the efficiency of the sweep of crude from the formation is diminished, sometimes to zero, when injection steam breaks through into the producing well. This condition is known as gravity override. Hot water which separates from the injected steam tends to sweep through the bottom portions of the heated interval while the steam vapor tends to override the hot water, because of differences in densities of the two fluids. As the hot water flows through the reservoir, heat is transferred to the rock and reservoir fluids. This results in a temperature transition from the hot water bank to cooler water ahead of the bank. In practice, this means an ordinary waterflood precedes the warm and hot water banks which results in reduced sweep efficiency and a gradual increase in residual oil saturation with distance from the injector. Because of the unfavorable viscosity ratio the efficiency of this waterflood will be poor. However, good recovery efficiency with steam in the upper portion of the heated interval will result in significant reductions in residual oil saturations. These differences in oil saturations will adversely affect the naturally-poor relative permeability ratio of steam and water. As a result, injected steam will tend to prematurely breakthrough into the offset producing wells without sweeping the entire heated interval. If this condition is permitted to continue, the production of reservoir fluids can drop to zero and only steam and water will be produced at the producing wells.
In steam flooding, the rate of steam injection is initially high so as to minimize heat losses to the cap and base rock with time. Frequently, this procedure results in the development of a highly permeable and relatively oil-free channel between injector and producer. Many times this channel develops near the top of the oil bearing rock. In this case, much of the injected heat is conducted to the cap rock as a heat loss, rather than being conducted to oil bearing sand where the heat is needed. In addition, the steam cannot displace oil efficiently since little oil is left in the channel. Consequently, neither the gas drive from the steam vapor nor the convective heat transfer mechanisms work efficiently. This is why much lower oil recovery results when a steam flood breaks through into the producing well.
Further, while some graphic illustrations of steam profiles between injection wells and producing wells represent that steam and hot fluids start all along the injection well, rise toward the top of the producing interval in the direction of the producing well and drop down near the producing well, it is now a common belief that such a profile is inaccurate. More than likely, once the steam has risen through the producing interval it will not drop down into the producing well when steam breakthrough occurs. This condition has been shown to exist by temperature profiles along a producing well. Such a condition further reduces the sweep efficiency of such a steam injection method.
Somewhat similarly, injected water as gas may pass more rapidly through relatively more permeable strata to producing wells reducing displacement of crude in less permeable strata to lower values or zero.
It has been suggested to inject a blocking barrier into the formation to reduce the loss of steam, water or gas through the breakthrough path. One such barrier is a foam as suggested in U.S. Pat. No. 3,412,793 issued to R. B. Needham on Nov. 26, 1968 for Plugging High Permeability Earth Strata. The highly permeable formation is temporarily plugged with a foam by introduction of steam and a foaming agent into the formation whereby a foam having steam as its gaseous phase is formed and, upon condensation of the steam due to loss of heat, the foam collapses. A similar procedure is shown in U.S. Pat. No. 4,086,964 issued to R. E. Dilgren et al. on May 2, 1979 for Steam-Channel-Expanding Steam Foam Drive. That patent suggests the addition of a noncondensible gas to the foam and injection into the steam channel to provide foam and a relatively high pressure gradient within the channel. Neither of these patents are believed to provide the relatively permanent solution to the gravity override breakthrough problems as is disclosed in the present application.
In copending application Ser. No. 289,550, now abandoned, by Stanley O. Hutchinson, for Foam and Particulate Material With Steam for Permeability Alteration in Subsurface formation, assigned to the same assignee as the present application, a method is proposed to alter the gravity override path within the formation by carrying into the formation particulate materials which will alter the permeability of the override path and thus encourage the flow of injection steam or hot fluids into the formations where reservoir fluids remain. The intention of the injection procedures is to recognize gravity override breakthrough and to then inject into that breakthrough path materials which will alter the permeability therein and then return to the injection procedure to reestablish communication between the injection fluids and the reservoir where the desired reservoir fluids remain. The particulate material is carried into the permeability override path with a low velocity fluid thus accomplishing the desired permeability alteration without damage to the well bore liner and without "bridging" in the formation.
It is suspected that the fine particulate materials that have previously been proposed for altering the permeability of the formation can be carried with produced and injected fluids into the production well and through the producing equipment. It is known that fine particulate material has returned to the injection well in a huff-and-puff operation and has damaged producing equipment by abrasion. Characteristicly, the steam-stimulated well requires pumping to bring the produced fluids to the earth's surface. The movement of the fine particulate materials with the fluids may result in abrasion damage to the pumping equipment if abrasive particulates are used.
The object of the present invention is the placement of particulate material in a subsurface earth formation in a manner to alter the permeability of the formation. The particulate material selected for the present invention is a material from the group of materials which will provide a non-abrasive characteristic for the previously injected particulate materials produced through the formation thus avoiding abrasive damage to subsurface and wellhead equipment used both in injection and producing wells.
A further object is the use of non-abrasive finely divided amorphous particulate material as an addition to injected gas, liquid or vapor for altering the permeability of a subsurface formation where a higher permeability passageway has been naturally or artificially created.
Further objects and features of the present invention will be readily apparent to those skilled in the art from the following specification describing preferred embodiment.